1. Field of the Invention
The present invention relates to a sheet thickness detection device disposed in a sheet conveying path for detecting the thickness of a sheet of paper and a sheet conveying device and an image forming apparatus having the same.
2. Description of the Related Art
Sheet thickness detection devices for detecting the thickness of a sheet of paper as described below have been available according to the related art.
As shown in FIG. 5, there is a sheet thickness detecting sensor 108 for detecting the thickness of a sheet by detecting the amount of a movement of a movable core 100 moving in accordance with the thickness of the sheet from a magnetic change. The movable core 100 is provided at one end of a rotatable lever 104 which is urged against a guiding upper guide 102 for guiding the sheet at another end thereof, and the movable core 100 moves in accordance with a displacement of the lever 104 at a time when the sheet passes through a gap between the guiding upper guide 102 and the lever 104 (JP-A-2001-199593).
According to this technique, one surface of a sheet is in contact with the detection lever 104, and the other surface of the sheet faces a surface of the guiding guide 102. As a result, for example, when the sheet has high rigidity and curls up, a gap is generated between the sheet surface and the surface of the guiding guide 102, and the thickness of the sheet may be overestimated.
Another detector detects thickness of a sheet of paper using an optical reflection type displacement sensor (JP-A-2003-112840).
However, since a sheet of paper has a thickness of about 0.05 to 0.3 mm, it has been necessary to use an expensive sensor for accurate detection.